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In the end I've usually settled for more diffraction rather than risk a totally screwed up picture. I'd also like to point out the uncertainty regarding depth of field made its way into my 35mm work.
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1.Situations where there is a lot of depth and multiple planes, and tilts and swings cannot be used:
·How do you decide where to focus?
·Do you use “conventional” depth of field rules?
·Do you focus on the near objects?
·Do you focus at a hyperfocal distance (ie focus on nothing)?
·Do you use Merklinger’s “object plane” method (usually resulting in an infinity bias)?
·Do you focus at infinity?
·How do you determine depth of field?
·Do you simply use the near-far focus method?

I don't use LF and don't practice the Scheimpflug laws. I can answer what I do regarding 135 as this is also what you seem to be interested in.

First of all, I'm very wary of DoF marks for serious work. The reasons are:

- The marks are generally set according to a circle of confusion a bit too tolerant for my taste: if using them, I tend to close 1 stop more, that is, close at f/11 while using DoF marks for f/8;

- Focus is some "binary" concept to me. It's either there, or not. Something in "acceptable" focus is typically just "tolerably" out of focus.

So what is the answer?

My personal answer, and YMMV, is that even in a situation where there is the need of an ample depth in focus plane, there always is one element of the picture that must be perfectly in focus. If that one element is perfectly in focus, the focus error in the other elements are more acceptable to the viewer and the scene looks natural.

To make an example: you have the landscape where you have the near field (let's say a stone 5 metre away), the middle field (let's say a tree 15 m away) and the background (let's say some mountains).

The normal approach in this kind of photography is: which is the right focus point and f/aperture which will give me an acceptable DoF so that everything, from the stone to the mountain, is acceptably in focus? By having recourse to some DoF tables or marks, one chooses the "optimal" focus point. This approach I don't follow.

This approach will lead to some focus point whereby none of the three elements is perfectly in focus. As I repeat, close is no cigar and acceptable is often a poor compromise.

My answer would be: focus on the tree. Do some reasoning about what is the f/aperture for the rock and mountains to be reasonably in focus. Remember they will never be "perfectly" in focus. But whatever decently close f/stop you use, the tree must be perfectly in focus.

The fact that there is an element perfectly in focus in the image makes the "acceptably in focus" elements, stone and mountains, much more acceptable to the eye (as acceptably in focus) than what would happen if no element were perfectly in focus (even if the rock or the mountains were a bit "more acceptably" in focus).

Stated in alternative terms: if nothing is perfectly in focus there is something wrong in the image. If one element is perfectly in focus, the mind sees as acceptably in focus also elements which are not perfectly in focus.